The invention relates generally to apparatus to transporting documents past one or more document processing stations. More particularly, the invention relates to pinch force generation at various drive wheels or capstans of document transport apparatus.
FIGS. 1a, 1b, 1c illustrate the basic components of a conventional document transport system for stopping a document 102 after traveling at high speed in transport 100 so that information can be printed on document 102 with document processing apparatus, such as a printer 104. Printing magnetic ink character (MICR) amount fields on a check is a typical example of documents being processed. However, this invention applies to any other device that requires a document to be transported accurately in order to process it.
FIGS. 1a, b, c illustrate the case of a relatively short document 102. In the document""s stopped position at printer 104, only one drive roller, in this case capstan 112, is in contact with the document 102. Typically, document 102 is moved at high speed up to a print station 104 with an entrance transport 106, usually running at a high, constant speed. A typical entrance transport includes an input drive roller 108 and a companion pinch roller 110, between which document 102 travels. When document 102 is in the grip of the capstan 112 and its associated pinch roller 114 only, capstan 112 and hence document 102 is decelerated to the desired stop position relative to the document processing station, in this example, print station 104.
Edge sensor 116 is positioned a known distance from the desired stop position. Motion of the capstan 112 is controlled by a single motor (not shown) which is a part of a servo feedback control loop. Such methods of positioning documents are well known to those practiced in the art of document processing.
After printing on document 102 using hammer bank 118, print drum 120 and ribbon 121 of print station 104, document 102 is accelerated up to the speed of the exit transport 122 by the capstan 112. The exit transport 122, usually running at high, constant speed, moves document 102 to other devices for further processing or to a document transport exit via drive roller 124 and its associated pinch roller 126.
Pinch rollers 110 and 126 are normally spring loaded against the entrance and exit drive rollers 108 and 124, respectively, and pinch roller 114 against the capstan 112 to provide drive force for the document 102. This is likewise common practice in the art.
During deceleration of document 102 by capstan 112, pinch roller 114 must also undergo this same deceleration. However, as a practical matter, pinch rollers, such as 114, have considerably more inertia than a document, such as a check. Therefore, the inertia of pinch roller 114 can carry document 102 with it and cause the document 102 to go past its intended stop position, if document 102 slips on capstan 112.
Previous practice increased the force on pinch roller 114 to help prevent document slippage or sliding with respect to capstan 112. However, large pinch forces can result in excessive loads on capstan 112, pinch rollers 110, 114 and 126 and their support systems and bearings, causing premature failure of these components. Large pinch forces also require capstan drive motors to provide large amounts of power thereby wasting energy.
The above problems with pinch rollers also apply during the document""s acceleration. In this case, document 102 won""t accelerate as fast as capstan 112. This, in turn, leads to two negative effects. First, documents behind document 102 being processed may crash into it. Second, document 102 may not get up to the exit transport speed before it enters the nip of the exit transport, thereby causing poor document control.
Accordingly, in one aspect of this invention, a document transport including at least one drive roller includes apparatus for providing pinch force to a document abutting the drive roller. A nozzle has an inlet and an outlet, the outlet facing the drive roller and spaced therefrom for permitting documents to pass therebetween. A source of compressed fluid, such as air, is coupled to the inlet of the nozzle thereby enabling it to provide pinch force pneumatically by a compressed fluid flow towards the drive roller.
In another aspect of the invention, a document transport system for carrying documents past a document processing station includes an entrance transport including at least one entrance drive roller adapted to propel documents into the transport system, a capstan positioned downstream of the at least one entrance drive roller, the capstan positioned upstream of the document processing station and adapted to propel documents into the document processing station, an exit transport including at least one exit drive roller adapted to propel documents away from the processing station, and a pneumatic pinch force generator positioned opposite at least one of the at least one entrance drive roller, the capstan and the at least one exit drive roller for applying pinch force to a document passing between the pneumatic pinch force generator and at least one of the at least one entrance drive roller, the capstan and the at least one exit drive roller.